Today there are a wide range of intravascular prostheses on the market for use in the treatment of aneurysms, stenosis, and other vascular irregularities. Balloon expandable and self-expanding stents are well known for restoring patency in a stenosed vessel, e.g., after an angioplasty procedure, and the use of coils and stents are known techniques for treating aneurysms.
Previously-known self-expanding stents generally are retained in a contracted delivery configuration using a sheath, then self-expand when the sheath is retracted. Such stents commonly have several drawbacks, for example, the stents may experience large length changes during expansion (referred to as “foreshortening”) and may shift within the vessel prior to engaging the vessel wall, resulting in improper placement. Additionally, many self-expanding stents have relatively large delivery profiles because the configuration of their struts limits further compression of the stent. Accordingly, such stents may not be suitable for use in smaller vessels, such as cerebral vessels and coronary arteries.
Other drawbacks associated with the use of coils or stents in the treatment of aneurysms is that the devices, when deployed, may have a tendency to straighten or otherwise remodel a delicate cerebral vessel, which may cause further adverse consequences. Moreover, such devices may not adequately reduce blood flow from the cerebral vessel into the sac of the aneurysm, which may increase the likelihood of rupture.
For example, PCT Publication WO 00/62711 to Rivelli describes a stent comprising a helical mesh coil having a plurality of turns and including a lattice having a multiplicity of pores. The lattice is tapered along its length. In operation, the plurality of turns are wound into a reduced diameter helical shape, then constrained within a delivery sheath. The delivery sheath is retracted to expose the distal section of the stent and anchor the distal end of the stent. As the delivery sheath is further retracted, subsequent individual turns of the stent unwind to conform to the diameter of the vessel wall.
The stent described in the foregoing publication has several drawbacks. For example, due to friction between the turns and the sheath, the individual turns of the stent may bunch up, or overlap with one another, when the delivery sheath is retracted. U.S. Pat. No. 4,768,507 to Fischell et al. and U.S. Pat. No. 6,576,006 to Limon et al., each describe the use of a groove disposed on an outer surface of an interior portion of the stent delivery catheter, wherein at least a portion of the stent is disposed within the groove to prevent axial movement during proximal retraction of the sheath.
While the delivery catheters disclosed in the foregoing patents prevent axial movement and bunching of the prosthesis during retraction of the sheath of the delivery catheter, those systems do not effectively address the issue of stent foreshortening. In particular, once the sheath of the delivery catheter is fully retracted, the turns of a ribbon-type stent may shift relative to one another within the vessel prior to engaging the vessel wall, resulting in inadequate coverage of the stenosis.
In view of the drawbacks of previously known ribbon-type stent delivery systems, it would be desirable to provide a delivery catheter that controls axial movement of a ribbon-type stent within the catheter during deployment.
It also would be desirable to provide a delivery catheter suitable for use with ribbon-type stents that provides a predictable amount of foreshortening of the stent during delivery, thereby improving accuracy of stent deployment.
It further would be desirable to provide a delivery catheter suitable for use with ribbon-type stents that mitigates foreshortening of the stent during delivery, and thus enhances the ability of a stent of predetermined length to provide adequate coverage of a stenosis.